A conventional transistor design may have source, drain, and gate structures. The output current of the transistor is modulated by controlling a voltage applied to the transistor's gate structure. In many conventional transistor designs, however, a capacitance forms between the transistor's gate and drain structures, reducing the gain and overall performance of the transistor.
The two main sources of a transistor's gate-to-drain capacitance can be an inter-electrode capacitance between the gate metallization and the drain metallization and a capacitive coupling between the gate and drain structures due to the space charge region in the semiconductor material. The space charge region in the semiconductor material extends from a point beneath the gate structure to the drain of the transistor.
One attempt to reduce this capacitance has been to place a conductor between the gate and drain structures. The conductor is electrically isolated from the substrate of the transistor by a dielectric or insulative layer, and electrically connected to the source. Such a conductive structure can be referred to as a field plate. When an electric potential is supplied to the field plate, the field plate operates to increase the breakdown voltage and reduce the inter-electrode capacitance of the transistor by redistributing the electric field at the gate edge of the transistor such that the gate-drain voltage is dropped across the dielectric layer instead of the semiconductor surface.
In conventional devices, however, difficulties in manufacturing processes have generally required that field plates be implemented as an additional metal layer formed over the transistor device and connected to the device's metal contacts. This implementation complicates both the transistor design and manufacturing process, increasing overall device cost.